Multi‐stimuli‐responsive self‐immolative polymer assemblies

Self‐immolative polymers (SIPs) undergo depolymerization in response to the cleavage of stimuli‐responsive end‐caps from their termini. Some classes of SIPs, including polycarbamates, have depolymerization rates that depend on environmental factors such as solvent and pH. In previous work, hydrophobic SIPs have been incorporated into amphiphilic block copolymers and used to prepare nanoassemblies. However, stimuli‐responsive hydrophilic blocks have not previously been incorporated. In this work, we synthesized amphiphilic copolymers composed of a hydrophobic polycarbamate SIP block and a hydrophilic poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) block connected by a UV light‐responsive linker end‐cap. It was hypothesized that after assembly of the block copolymers into nanoparticles, chain collapse of the PDMAEMA above its lower critical solution temperature (LCST) might change the environment of the SIP block, thereby altering its depolymerization rate. Self‐assembly of the block copolymers was performed, and the depolymerization of the resulting assemblies was studied by fluorescence spectroscopy, dynamic light scattering, and NMR spectroscopy. At 20 °C, the system exhibited a selective response to the UV light. At 65 °C, above the LCST of PDMAEMA, the systems underwent more rapid depolymerization, suggesting that the increase in rate arising from the higher temperature dominated over environmental effects arising from chain collapse. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1868–1877     

Biocompatibility evaluation of self‐assembled micelles prepared from poly(lactide‐co‐glycolide)‐poly(ethylene glycol) diblock copolymers

In this work, a series of PLGA‐PEG diblock copolymers were synthesized by ring‐opening polymerization of L‐lactide and glycolide using mPEG as macroinitiator and stannous octoate as catalyst. Spherical micelles were obtained from the various copolymers by using co‐solvent evaporation method. The biocompatibility of micelles was evaluated with the aim of assessing their potential in the development of drug delivery systems. Various aspects of biocompatibility were considered, including MTT assay, agar diffusion test, release of cytokines, hemolytic test, dynamic clotting time, protein adsorption in vitro, and zebrafish embryonic compatibility in vivo. The combined results revealed that the micelles present good cytocompatibility and hemocompatibility in vitro. Moreover, the cumulative effects of micelles throughout embryos developing stages have no toxicity in vivo. It is thus concluded that micelles prepared from PLGA‐PEG copolymers present good biocompatibility as potential drug carrier.     

Elasticity‐Dependent Fast Underwater Adhesion Demonstrated by Macroscopic Supramolecular Assembly

Macroscopic supramolecular assembly (MSA) is a recent development in supramolecular chemistry to associate visible building blocks through non‐covalent interactions in a multivalent manner. Although various substrates (e.g. hydrogels, rigid materials) have been used, a general design rule of building blocks in MSA systems and interpretation of the assembly mechanism are lacking and are required. Herein we design three model systems with varied elastic modulus and correlated the MSA probability with the elasticity. Based on the effects of substrate deformability on multivalency, we have proposed an elastic‐modulus‐dependent rule that building blocks below a critical modulus of 2.5 MPa can achieve MSA for the used host/guest system. Moreover, this MSA rule applies well to the design of materials for fast underwater adhesion: Soft substrates (0.5 MPa) can achieve underwater adhesion within 10 s with one order of magnitude higher strength than that of rigid substrates (2.5 MPa).     

Electrostatic Layer‐by‐Layer Assembly of Polycation and DNA Multilayer Films by Real‐time Surface Plasmon Resonance Technique

The assembly of alternating DNA and positively charged poly‐(dimethyldiallylammonium chloride) (PDDA) multilayer films by electrostatic layer‐by‐layer adsorption has been studied. Real time surface plasmon resonance (BIAcore) technique was used to characterize and monitor the formation of multilayer films in solution in real time continuously. The results indicate that the uniform multilayer can be obtained on the poly‐(ethylenimine) (PEI) coated substrate surface. The kinetics of the adsorption of DNA on PDDA surface was also studied by real‐time BIAcore technique, and the observed rate constant was calculated using a Langmuir model (k_obs = (1.28 ± 0.08) × 10^?2s^?1).     

Stimuli-responsive multilayer chitosan hollow microspheres via layer-by-layer assembly

Novel stimuli-responsive multilayer chitosan hollow microspheres with chitosan as the unique component have been fabricated by the sequential layer-by-layer electrostatic assembly technique from the sacrificial templates (polystyrene sulfonate, PSS) with chitosan (CS) as the polycation and carboxymethyl chitosan (CMCS) as the polyanion, respectively. Their hollow structure was confirmed by the TEM analysis. The DLS analysis indicated that the multilayer chitosan microcapsules were pH and ionic strength dual-responsive. Due to the biocompatibility of the single component chitosan used, the multilayer chitosan microcapsules are expected to be used in the controlled release of drugs.     

Controlling aggregate formation in conjugated polymers by spin‐coating below the critical temperature of the disorder–order transition

Aggregates – that is short‐ranged ordered moieties in the solid‐state of π‐conjugated polymers – play an important role in the photophysics and performance of various optoelectronic devices. We have previously shown that many polymers change from a disordered to a more ordered conformation when cooling a solution below a characteristic critical temperature . Using in situ time‐resolved absorption spectroscopy on the prototypical semiconducting polymers P3HT, PFO, PCPDTBT, and PCE11 (PffBT4T‐2OD), we show that spin‐coating at a temperature below can enhance the formation of aggregates with strong intra‐chain coupling. An analysis of their time‐resolved spectra indicates that the formation of nuclei in the initial stages of film formation for substrates held below seems responsible for this. We observe that the growth rate of the aggregates is thermally activated with an energy of 310 meV, which is much more than that of the solvent viscosity (100 meV). From this we conclude that the rate controlling step is the planarization of a chain that is associated with its attachment to a nucleation center. The success of our approach for the rather dynamic deposition method of spin‐coating holds promise for other solution‐based deposition methods. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 532–542     

Electrochemical Fabrication of Nanostructured Surfaces for Enhanced Response

The objective of this work is to explore approaches to enhance electrochemical signals through sequential deposition and capping of gold particles. Gold nanoparticles are electrodeposited from KAuCl₄ solution under potentiostatic conditions on glassy carbon substrates. The number density of the nanoparticles is increased by multiple deposition steps. To prevent secondary nucleation processes, the nanoparticles are isolated after each potentiostatic deposition step by self‐assembled monolayers (SAMs) of decanethiol or mercaptoethanol. The increasing number of particles during five deposition/protection rounds is monitored by assembling electroactive SAMs using a ferrocene‐labeled alkanethiol. A precise estimation of the surface area of the gold nanoparticles by formation of an oxide layer on gold is difficult due to oxidation of the glassy carbon surface. As an alternative approach, the charge flow of the electroactive SAM is used for surface measurement of the gold surface area. A sixfold increase in the redox signal in comparison to a bulk gold surface is observed, and this increase in redox signal is particularly notable given that the surface area of the deposited nanoparticles is only a fraction of the bulk gold surface. After five rounds of deposition there is a gold loading of 1.94 μg cm^?2 of the deposited nanoparticles as compared to 23.68 μg cm^?2 for the bulk gold surface. Remarkably, however, the surface coverage of the ferrocene alkanethiol on the bulk material is only 10 % of that achieved on the deposited nanoparticles. This enhancement in signal of the nanoparticle‐modified surface in comparison to bulk gold is thus demonstrated not to be attributable to an increase in surface area, but rather to the inherent properties of the surface atoms of the nanoparticles, which are more reactive than the surface atoms of the bulk material.